The invention relates to a ground connection for an aluminum component, especially a vehicle body component, having a grounding bolt which is fastened to said component, with the interposition of an adapter that extends over the surface and which is composed of a material which exhibits greater strength than the aluminum component and differs in the electrochemical potential series, especially steel, and having a thread element which clamps the cable shoe of the ground conductor on a corresponding contact area of the ground connection.
From DE 102 49 918 A1, a ground connection of this kind is known for aluminum components with a grounding bolt made of steel, wherein an adapter in the form of a sleevelike spacer made from a material compatible with the aluminum component, i.e., preferably also aluminum, is interposed between the bolt and the aluminum component. The grounding bolt is connected in a rotationally firm manner to the spacer by form fit and/or friction locking. The problem with this known ground connection is its pronounced tendency to corrode at the interface between the steel bolt and the aluminum adapter and the resulting electrical junction resistance to the cable shoe of the ground conductor for the sometimes extremely high current flow of up to 1000 A or more. Furthermore, the thread element needs to be tightened with a very large torque in relation to its size, in order to tighten the cable shoe of the ground conductor in mechanically firm manner to the ground connection, but on account of the material of the form fit and/or friction locking connection of the grounding bolt to the aluminum adapter it has limited torque strength and therefore often does not withstand the required tightening torque.
The problem which the invention proposes to solve is to modify a ground connection of the kind mentioned at the outset so that it guarantees a permanently high functional reliability by a simple manufacturing method.
This problem is solved according to the invention by the ground connection in accordance with embodiments of the invention.
According to the invention, the functional reliability of the ground connection is significantly improved in several respects. Thus, the loading strength of the ground connection and thus the permissible tightening torque of the thread element are significantly increased in that the interface between grounding bolt and adapter is cohesive, i.e., formed either as a single piece as preferred or as a thermal welding connection, and the interface between adapter and component has a large surface area and a high level of load strength as a combined connection welded with aluminum as additional material at the component side and soldered with the zinc plating as flux on the adapter side. At the same time, the ground connection has a significantly improved corrosion resistance, because the grounding bolt and the adapter are the same material and therefore joined together without an electrochemical potential difference and the adapter is held without contact with the component at the other interface and the intervening gap is bridged by a controlled material transfer in the welded/soldered connection. Finally, the ground connection also presents a very low electrical junction resistance, since in addition to the high electrical conductivity of the materials used the individual connection sites can also easily be dimensioned with a large flow cross section, suitable to the required current loads. Furthermore, the ground connection according to the invention is easy to produce, suitable for serial production, and easy to install.
Another fabrication simplification consists in that the welded/soldered connection is produced as a fillet weld running continuously in a straight line between the adapter edge and the component.
According to another aspect, the adapter is preferably formed as an adapter plate freely protruding beyond the welded/soldered connection, parallel to the surface extension of the component and formed at the free end connected to the grounding bolt. In this way, on the one hand vibrations introduced at the component side are transmitted to the grounding bolt attenuated on their way across the adapter plate, which is connected in a vibration-capable manner, and on the other hand a direct adapter contact with the component is avoided not only at the welded/soldered connection, but also at the rest of the adapter surfaces, for corrosion protection reasons.
If, in certain applications, especially when the ground connection is situated in the exterior region of a motor vehicle, the contact-free attachment of the adapter to the component in combination with the controlled material transfer at the welded/soldered connection in themselves are not enough for a constantly effective corrosion protection, the ground connection can additionally be coated with a corrosion protection layer.
It has proven to be especially advantageous to produce the welded/soldered connection by way of the known cold metal transfer method with changing polarity and in this case, to organize the polarity change in variable manner according to the particular material pairing at the welded/soldered connection.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.